A variety of medical diagnostic procedures involve tests on biological fluids, such as blood, urine, or saliva, and are based on a change in a physical characteristic of such a fluid or an element of the fluid, such as blood serum. The characteristic can be an electrical, magnetic, fluidic, or optical property. When an optical property is monitored, these procedures may make use of a transparent or translucent device to contain the biological fluid and a reagent. A change in light absorption of the fluid can be related to an analyte H concentration in, or property of, the fluid.
In many such devices, fluid is introduced into the device at one location but analyzed at another. In such devices, movement of the introduced fluid from the introduction location to the measurement location is necessary. As such, these devices require a means for moving fluid from the introduction site to the measurement site.
A variety of different design configurations have been developed to provide for this fluid movement. One type of device relies on capillary action to move fluid through the device, where the fluid paths through the device are dimensioned to provide for this capillary action. Other designs include those intended for use with gravity, those intended for use with injection of the sample under pressure, and the like.
In one class of fluidic test devices or strips that find use in various assay applications, fluid is moved through the device from the point of introduction by negative pressure, where the negative pressure is typically provided by a compressible bladder. Such devices include those described in U.S. Pat. No. 3,620,676; U.S. Pat. No. 3,640,267 and EP 0 803 288.
With these types of devices, there is a need to be able to actuate the bladder in a reproducible and uniform manner, such that errors in the assay are not introduced through variations in bladder volume through the compression and decompression cycle.
Relevant Literature
References of interest include: U.S. Pat. Nos. 3,620,676; 3,640,267; 4,088,448; 4,426,451; 4,868,129; 5,104,813; 5,230,866; 5,700,695; 5,736,404; 5,208,163; and European Patent Application EP 0 803 288.